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Questions and Answers
What is the basic structural unit of chromatin?
What is the basic structural unit of chromatin?
- Nucleosome (correct)
- Chromosome
- Ribosome
- Centriole
What is the role of histones?
What is the role of histones?
Histones are basic proteins that help package and organize DNA into a compact structure called chromatin. They bind to DNA, forming a nucleosome, which acts as a basic unit of chromatin.
What distinguishes euchromatin from heterochromatin?
What distinguishes euchromatin from heterochromatin?
- Euchromatin and heterochromatin are both densely packed and transcriptionally inactive.
- Euchromatin is more densely packed and is transcriptionally inactive, while heterochromatin is loosely packed and more active.
- Euchromatin and heterochromatin are both loosely packed and transcriptionally active.
- Heterochromatin is more densely packed and is transcriptionally inactive, while euchromatin is loosely packed and more active. (correct)
What is meant by the term "differentiation"?
What is meant by the term "differentiation"?
The nucleus is surrounded by a single membrane.
The nucleus is surrounded by a single membrane.
What are the three main recognized components of the nucleus?
What are the three main recognized components of the nucleus?
How do molecules larger than 9 nm pass through the nuclear pore?
How do molecules larger than 9 nm pass through the nuclear pore?
What is the function of the nucleolus?
What is the function of the nucleolus?
What is the function of the nuclear envelope?
What is the function of the nuclear envelope?
The nucleus produces proteins.
The nucleus produces proteins.
Flashcards
Cell Nucleus Function
Cell Nucleus Function
Contains DNA blueprints for cell structures and activities, and processes RNA (ribosomal, messenger, transfer).
Chromatin
Chromatin
DNA and proteins coiled into thread-like strands.
Nucleosome
Nucleosome
Basic structural unit of chromatin; DNA wrapped around histone proteins.
Histones
Histones
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Heterochromatin
Heterochromatin
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Euchromatin
Euchromatin
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Nuclear Envelope
Nuclear Envelope
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Nuclear Pores
Nuclear Pores
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Nucleolus
Nucleolus
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Cell Cycle
Cell Cycle
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Interphase
Interphase
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G1 Phase
G1 Phase
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S Phase
S Phase
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G2 Phase
G2 Phase
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Mitosis
Mitosis
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Sex Chromatin
Sex Chromatin
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G0 Phase
G0 Phase
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Differentiation
Differentiation
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Ribosomes
Ribosomes
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Study Notes
Nucleus and phases of cell cycle
- The nucleus contains the blueprint for all cell structures and activities, encoded in the DNA of chromosomes. It also contains the molecular machinery for DNA replication and the synthesis and processing of RNA (rRNA, mRNA, tRNA).
- The nucleus itself does not produce proteins; proteins needed for nuclear activities are imported from the cytoplasm.
- The nucleus usually appears as a rounded or elongated structure in the cell center.
- The nucleus's main components are the nuclear envelope, chromatin, nucleolus, and nuclear matrix.
- The nucleus appears intensely stained dark blue or black in common hematoxylin and eosin-stained preparations.
Nuclear Envelope
- The nucleus is surrounded by two parallel membranes, separated by a space called the perinuclear cisterna.
- The paired membranes and the intervening space form the nuclear envelope.
- The nuclear envelope is continuous with the endoplasmic reticulum, shown by polyribosomes attached to the outer membrane.
- Nuclear pores exist where the inner and outer membranes of the envelope fuse, allowing substances to pass between the nucleus and cytoplasm.
- Only ions and small molecules pass freely through nuclear pores; larger molecules require an active transport process.
Chromatin
- Chromatin is composed mainly of DNA coiled around basic proteins called histones.
- The basic structural unit of chromatin is the nucleosome.
- Four types of histones form the core of a nucleosome, with DNA base pairs wrapped around them.
- Linker DNA connects adjacent nucleosomes, and another histone type is bound to this DNA.
- Chromatin can exist in two readily distinguishable forms: euchromatin (genetically active) and heterochromatin (genetically inactive).
- Heterochromatin appears electron-dense and basophilic.
- Euchromatin appears electron-lucent and lightly stained.
- The proportion of heterochromatin to euchromatin affects the nucleus's overall intensity of staining, which can be used to interpret its functional state.
Nucleolus
- The nucleolus is a spherical structure rich in rRNA and proteins, appearing basophilic.
- It is the site where ribosomal subunits are synthesized.
- Ribosomal proteins are synthesized in the cytoplasm and join with rRNAs in the nucleolus.
- Ribosomal subunits then migrate to the cytoplasm through nuclear pores.
Cell Cycle
- The cell cycle is a series of events preparing a cell to divide into two daughter cells.
- Interphase is the long period of growth and DNA replication before cell division.
- Interphase consists of three stages: G1, S, and G2.
- G1: Cell growth, synthesis of macromolecules essential for DNA duplication.
- S: DNA is duplicated.
- G2: Cell undergoes preparations for mitosis.
- Mitosis is the shorter period where the cell's nucleus divides, leading to two daughter cells.
- Cells that exit the division cycle enter a resting stage, called G0.
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